The invention relates to a measuring arrangement for brake application force measurement of a disc brake. It also relates to a corresponding disc brake.
Disc brakes can have different measuring arrangements for detecting a brake application force, wherein for this purpose, for example, pressure sensors are used in a hydraulic brake. However, a disc brake on a vehicle is subjected to relatively extreme operating conditions which can influence in different ways a measurement variable which correlates with the brake application force of the disc brake.
A measuring arrangement for brake application force measurement of a disc brake is described, for example, in DE 10 2009 041 951. In the disc brake in said document, the brake application force sensor is arranged in its observation direction in an extension of the displacement travel of the measurement object or the target object section thereof. Although this measuring arrangement has proven effective in practice, malfunctions can occur if contamination or other particles, which no longer permit contactless measurement, accumulate between the brake application force sensor and the measurement object or the target object section thereof. In such cases, the contamination or the other particles bring about a risk of contact between the brake application force sensor and the measurement object or the target object section thereof which are displaced with respect to one another. In the case of further displacement, a faulty signal is then output via the evaluation unit. The same fault occurs if the brake application force sensor and the measurement object or the target object section thereof are in direct contact with one another. This can be caused by incorrect adjustment of the measuring arrangement during its installation, with the result that the measuring arrangement cannot detect the entire possible displacement travel of the caliper head and caliper back of the brake caliper.
The object of the present invention is therefore to make available an improved measuring arrangement. A further object is to provide an improved corresponding disc brake.
This and other objects are achieved by a measuring arrangement, and a corresponding disc brake, having: a) two components of the disc brake which can be moved, in particular displaced, relative to one another along a travel path when the brake application force is applied, b) at least one brake application force sensor having a housing; c) a measurement object which is one of the two components or can be connected permanently to one of the two components and has at least one element or at least one target object with at least one such element for contactless interaction with the brake application force sensor; and d) an evaluation unit, wherein e) the brake application force sensor is designed to detect displacement of the measurement object along the travel path with the evaluation unit for converting the detected displacement into a measurement variable as a measure of the brake application force, f) the brake application force sensor and the measurement object can be attached to the respective component of the two components in such a way that they can be removed again, and g) the brake application force sensor is arranged outside the travel path of the measurement object and with its observation direction at a right angle to the travel path.
An advantageous feature of the invention is that the brake application force sensor and the measurement object can be attached to the respective component of the two components in such a way that they can be removed again. This results in simple mounting and a short replacement time during maintenance and servicing, wherein at the same time the accuracy of the determined measurement variable is retained. The field of application is enlarged and comprises disc brakes of any design, even those with self-energization.
Accordingly, a measuring arrangement for brake application force measurement of a disc brake preferably has the following: two components of the disc brake which can be moved, in particular displaced, relative to one another along a travel when the brake application force is applied, at least one brake application force sensor having a housing; a measurement object, which is one of the two components or can be connected permanently to one of the two components, and has at least one element or at least one target object with at least one such element for contactless interaction with the brake application force sensor; and an evaluation unit, wherein the brake application force sensor is designed to detect displacement along the travel with the evaluation unit for converting the detected displacement into a measurement variable as a measure of the brake application force, and wherein the brake application force sensor and the measurement object can be attached to the respective component of the two components in such a way that they can be removed again. In this context the brake application force sensor is arranged outside the travel of the measurement object and with its observation direction or its longitudinal axis at a right angle to the travel.
As a result, the situation is advantageously avoided in which the measurement object is displaced with its front onto the brake application force sensor and, under certain circumstances, even makes contact with it at the front, which would result in falsification of measured values. According to the invention, the measurement object is instead displaced in front of the brake application force sensor without the risk of a collision.
In one advantageous embodiment of the measuring arrangement, the element is made of metal and the brake application force sensor is embodied as an eddy current sensor. The brake application force sensor is preferably a Hall sensor or is embodied as an inductively operating sensor. In this way, contactless measurement of the displacement travel is made possible in a way which has little susceptibility to faults. The brake application force sensor particularly preferably has a plurality of, preferably three, coils, wherein difference signals of a second and third coil are used to correct interference signals. In this way, a correction of a signal of a first coil can be carried out, for example in order to obtain an output signal of the brake application force sensor which is linear as a function of the travel.
In one advantageous refinement of the measuring arrangement, the element is constructed with a contour, as a result of which the brake application force sensor picks up a signal which changes with the displacement travel. In this way, the signal can also be influenced as a function of the travel, for example in order to linearize said signal or to obtain other advantageous curve profiles between the travel and the output signal.
In a further refinement of the measuring arrangement, other measuring principles than the previously mentioned principle of an eddy current sensor can be used in the brake application force sensor.
The brake application force sensor and the measurement object can be attached to the respective component of the two components in a centered and/or positively locking fashion and in such a way that they can be removed again. As a result, the mounting time is shortened, wherein orientation times are reduced to a minimum. The brake application force sensor can advantageously be attached to the caliper head and the measurement object can be attached to the second component in a centered and/or positively locking fashion and in such a way that they can be removed again.
The brake application force sensor can be permanently connected to the caliper head and is arranged at a distance from the element of the measurement object with the observation direction at a right angle to the displacement direction of the measurement object in such a way that the free end of the measurement object is moved past the brake application force sensor at a constant distance during its brake application force-induced displacement.
A pickup device with at least one coil and an amplifier device can be arranged in the housing of the brake application force sensor. This arrangement is advantageous since in this way the detected measurement variable signal can be amplified in the shortest way without interference influences by electromagnetic fields from the outside. In order to increase the immunity to interference additionally with respect to moisture and dust, the housing can be hermetically sealed. In one embodiment, the housing is manufactured, for example, from a plastic such as, for example, glass-fiber-reinforced polyamide.
The brake application force sensor is oriented with the coil of the pickup device in a pickup longitudinal axis at a right angle to the element of the measurement object. This can be embodied, for example, easily by means of a centering device which forms positive engagement by means of surfaces, edges, centering pins, centering bolts or the like.
The brake application force sensor has a measuring range which is larger than the maximum relative displacement of the two components with respect to one another, brought about by the brake application force, by amounts equal to the installation tolerances and thermally induced changes in length. As a result, influencing as a result of interference variables such as changes in length and installation tolerances are largely reduced.
An end face of the brake application force sensor can be arranged at a distance from the element of the measurement object, between 0 mm and 10 mm, preferably between 0.5 mm and 6.5 mm. Eddy current sensors are available which also supply a high-accuracy signal at a very short distance.
In order to adapt to the surroundings, the brake application force sensor can be designed to output a sensor signal which can be calibrated to the material of the measurement object, of the target object, the material of the surroundings of the measurement object and/or of the target object and/or the geometry of the measurement object and/or of the target object. In this context, surface coatings of the end face of the brake application force sensor and of the element of the measurement object can also be taken into account. The material of the housing of the brake application force sensor can also be included in the calibration. For this purpose, the evaluation unit has, for example, a memory in which corresponding values are stored in table form, calibration being made possible in a simple way on the basis of said values. This memory can also contain values which can be used to output a temperature-compensated sensor signal and/or for a zero point adjustment of a sensor signal which is to be output.
The zero point corresponds here to the state of the unactivated brake which serves as a reference for any braking operation. This zero point can be displaced by a small amount during operation (as a result of vibrations, temperature expansion, etc.) and to a relatively large extent during maintenance and servicing (for example, change of brake pads). The absolute value of the zero point is not significant owing to linearization of the sensor signal. The brake application force sensor can therefore also be designed to output a linearized sensor signal by virtue of the fact that the associated values are stored in the evaluation unit. The linearization of the sensor signal can be embodied with respect to a change in position of the measurement object, target object and/or the brake application force.
In one embodiment, the pickup device, the amplifier device and the evaluation unit can be arranged in the housing, which results in a compact design.
In an alternative embodiment, the pickup device can be arranged in the housing. In this way, it is then possible for only the coil to be then present in the housing, which as a result becomes considerably smaller. In this context, further switching units of the pickup device, the amplifier device and the evaluation unit can be arranged separately therefrom. This can be integrated, for example, in a wear sensor unit of the brake or in a control unit. This can make simplified routing of the cable possible, with combination of cables, which reduces installation expenditure.
In another alternative, the pickup device and the amplifier device can be arranged in the housing, wherein the evaluation unit can be arranged in a wear sensor unit of the disc brake. In this context, the software of the evaluation unit can be a component of the software of the wear sensor unit, which also entails savings in terms of space and components.
In this way, the brake application force sensor can be provided with at least one permanently connectable connecting line and/or output line, and/or at least one connecting line and/or output line which can be connected via plug-type connector devices. The resulting combination of cables with the wear sensor unit or other units of the brake can be led onwards as a common cable to an EBS control unit.
A cable combination of the sensor cable and of a wear sensor cable is also possible, and this in turn reduces installation expenditure and installation space. The sensor cable can, of course, also be connected directly to a brake control unit.
The housing can easily be attached to one of the components and/or to a base plate of the disc brake in a simple manner by use of at least one attachment element directly and/or via at least one clip. For the purpose of rapid mounting and dismounting, the housing can also be screwed.
The measurement object can be embodied as a brake pad holding bracket which can be permanently connected to the one of the two components of the disc brake, in particular to the caliper back and which has the at least one end face or the at least one target object with at least one end face. The target object can be connectable directly to the brake pad holding bracket, directly or via a holding element. In this way, the target object, which is metallic or has a metallic element, can be screwed on, riveted on, welded on or joined on in some other way. It can be embodied in one piece with the pad holding bracket. Of course, the pad holding bracket can have more than one metallic element or more than one target object. As a result of the fact that the measuring arrangement is partially arranged on the pad holding bracket, or the pad holding bracket is part of the measuring arrangement, simple replacement possibilities during maintenance and servicing of the brake are obtained. Retrofitting of a brake around the measuring arrangement is also simplified.
In order to increase the measuring accuracy, the pad holding bracket can be attachable with a centering device to the one component. Nevertheless, the pad holding bracket can be replaced and removed with simple measures. Such securing will occur at least in the measuring direction of the sensor. The measuring direction is here the direction in which the pickup longitudinal axis of the sensor extends, with the result that displacement of the measurement object transversely with respect to its pickup longitudinal axis is detected by the sensor.
In order to bring about positive guidance, i.e. without a transverse offset, sagging etc., the pad holding bracket can be guided in a displaceable fashion with a guide device on the other component, in particular on the caliper head for the positive guidance in the direction of the travel. The pad holding bracket is therefore not rigidly attached to the other component, in particular to the caliper head of the disc brake, and is at least freely movable in the measuring direction of the sensor, with the result that the target object is moved past during the brake application force build up during the build up of brake application force by the coil of the sensor. This embodiment can be constructed in such a way that the pad holding bracket is restricted in its freedom of movement or in its degrees of freedom with respect to the brake disc in the radial direction and/or in the circumferential direction by, for example, correspondingly shaped surfaces on the brake caliper and/or base plate of the disc brake. The attachment of the pad holding bracket on the caliper back can therefore prevent pivoting movements of the target object on said caliper back transversely with respect to the pickup longitudinal axis of the coil of the sensor. As a result, the freedom of movement of the target object can be restricted with respect to the brake disc, in the radial direction and/or in the circumferential direction.
The attachment of the pad holding bracket on the caliper back can be, for example, a bolt connection, a screw connection, a combination thereof or with additional positive engagement.
For the sake of simplified calibration, the pad holding bracket and the target object can be manufactured from one material which has fixed properties for the calibration.
So that the measurement remains precise in the event of possible pivoting movements of the target object or of the pad holding bracket, the element can be embodied in a planar fashion, in particular with a planar face positioned perpendicularly with respect to the pickup longitudinal axis. As a result, this ensures that the distance between the brake application force sensor and the element of the target object or the target object itself does not change in the event of pivoting movements of the target object or of the pad holding bracket.
A brake application force sensor for a measuring arrangement as described above is embodied as described above.
A brake pad holding bracket can be used as described for a measuring arrangement above.
A disc brake according to the invention having a brake caliper which engages over a brake disc and has a caliper head and caliper back connected thereto, wherein brake pads which can be pressed onto the brake disc on both sides and are secured radially by way of a pad holding bracket are mounted in the brake caliper, characterized in that said disc brake has the measuring arrangement specified above. The measuring arrangement measures the change in the span length of the brake caliper which occurs when a clamping force acts, as a relative displacement of the free end of the second component, serving as a measurement object, relative to the caliper head. In this context, the brake application force sensor is arranged with its observation direction at a right angle to the longitudinal axis of the brake disc and therefore to the displacement direction of the free end of the second component.
In one embodiment, the disc brake has a brake caliper which connects, in the manner of a frame, a caliper head which is arranged on the activation side parallel to the disc brake to a caliper back, located on the opposite side of the brake disc, via tie rods which are arranged spaced apart in parallel and longitudinally with respect to the brake disc rotational axis. In this context, the mounting opening which is formed by the spacing apart of the tie rods is dimensioned to be so large that the brake pads are freely accessible and removable for the purpose of replacing them owing to wear, and when a clamping force is applied the distance between the caliper head and the caliper back is changed virtually in proportion to this clamping force.
In a further refinement, the disc brake has a component which bridges the mounting opening in the axial direction and parallel to the tie rods approximately centrally and is secured to the caliper back by means of an attachment element, and is supported on the caliper back against radial and, under certain circumstances, also tangential displacement in such a way that axial displacement of the free end of this second component is possible.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.